1. Field of the Invention
This invention relates to computer programs for modeling of hydraulics systems, and in particular, software for modeling of sewer and storm water systems.
2. Background Information
A typical sewer and storm water drainage system consists of a labyrinth of underground pipes leading from homes and buildings to a municipal sewage network that may include large tunnels and open channels, as well as an above ground system of drainage and runoff areas at roadsides, natural waterways and the like that lead to sewer openings and manholes. All of these are connected at junctions and interchanges that can include various hydraulic structures and natural barriers. Moreover, with ever increasing urbanization and urban renewal, there is an concomitant increase in drainage and water quality requirements, and thus, sanitary sewer and storm water systems are becoming even more complex, and yet more important to the growing communities that these systems serve.
The hydraulic characteristics of a complex sewer and storm drainage system often exhibit many complicated features, such as backwater effects from a downstream boundary or from hydraulic structures. The variety of structures that can be present in such a system is practically unlimited. The hydraulic structures can include culverts, bridges, weirs, spillways, contractions and expansions, either natural or constructed. There are also confluence interactions at junctions of a pipe network, interchanges between surcharged pressure flow and gravity flow conditions, street-flooding from overloaded pipes, as well as bifurcated pipe networks.
To better understand the complicated hydraulic features presented by such complex systems and to accurately simulate flows in this type of complicated sewer or storm water system, a software model is used as a tool to design, simulate and/or analyze these systems. To describe the complex hydraulic structures and flows, hydrodynamic approaches and unsteady flow models are needed. As part of the simulation, system behavior, including time variations in sanitary and storm water drainage flow events are also becoming of more interest to the engineering community.
Conventionally, in order to simulate unsteady flows in sewer or storm water drainage systems, numerical computational techniques have been the primary tools for such calculations. The results from numerical models are widely used for planning, designing and operational purposes. As noted, since an urban drainage system can be composed of thousands of pipes and many hydraulic structures, the hydraulics in many sewer and storm systems can exhibit very complicated flow conditions. The numerical stability, computational performance, capabilities and robustness and handling of such complicated is hydraulic conditions with computational accuracy are all factors that must be taken into account when engineers select a model for practical engineering use.
Many numerical models have been developed to simulate unsteady flows in sewer and storm water systems. Many are based on explicit numerical schemes. Some are based on implicit schemes and limitations exist for most of such models. Many models include using a steady system model and apply approximation techniques and case wise steady flow combinations, to approximate unsteady flow conditions. This has disadvantages in that the approximation is not entirely accurate.
Other numerical schemes used to simulate unsteady flows in sewer/drainage systems include solving complete dynamic equations. Most dynamic models have been developed using one of the following different numerical techniques: a) characteristic methods; b) explicit finite-difference schemes; and c) implicit finite-difference schemes (with six points or four points). Among these techniques, the implicit methods have the advantage of maintaining good stability for large computational time steps and exhibit robustness in modeling very complex situations, such as interchanges between gravity flows and pressure flows, pipe network flow and storage effect for street flooding, bifurcated pipe networks, flow regime changes between subcritical and supercritical conditions and the like.
Of the various implicit, finite-difference schemes, a weighted four-point scheme has been used in a United States National Weather Service Dynamic River Routing Model (FLDWAV) (sometimes referred to as “FLOODWAVE”), which is commercially available. It has been successfully used with unequal distance steps.
There remains a need, therefore, for a software program for developing a model of a sanitary sewer and storm drainage systems that meets the increasingly difficult challenges of modeling complicated unsteady flows in large, complex sewer and storm water systems. It is thus an object of the present invention to provide a method and software system for developing a model for unsteady flows in sewer and storm water systems that exhibits excellent computational performance, numerical stability and robustness.